Contents and associations of rare earth elements and yttrium in biomass ashes

Abstract

The contents and associations of 14 rare earth elements and Y (REY), as well as the phase-mineral and chemical composition of biomass ashes (BAs) from eight biomass varieties were studied. An elucidation of the REY contents in BAs was conducted and a comparison with coal ashes (CAs) was performed. The correlations and associations of REY with major and minor elements, and different mineral classes in BAs are given. It was found that REY commonly have about one order of magnitude lower bulk concentrations in BA than those in CA. The distribution of REY in BAs is strongly dependent on the plant species and their source, and the different inorganic ash types. The individual REY show numerous strong and significant positive correlations; however, three major associations can be divided according to these correlations, namely: (1) light Ce, La, Nd, and Pr with Al2O3 + Fe2O3 + TiO2, Al, phosphates, and Ti; (2) medium Y with carbonates, oxides and hydroxides, and K; and (3) light Sm, medium Dy, Eu, Gd and Tb, and heavy Er, Ho, Lu, Tm and Yb with Si and silicates. BA is a less prospective resource for a recovery of REY than CA according to their bulk concentrations; however, BAs are abundant in water-soluble components and their solutions may be used for REY recovery. The data also indicate that the low REY concentrations in BA would not have potential environmental and health concerns excluding their occurrence in mobile forms and in some radioactive silicate and phosphate minerals.